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Thread: Looking for a creative solution: USB bus still powered after CPU is off

  1. #1
    Maximum Bitrate S4Per's Avatar
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    Looking for a creative solution: USB bus still powered after CPU is off

    Hi All,
    Based on some of the stuff I posted yesterday, here's the latest, or better said - my core problem at this point.

    My Shuttle PC keeps the USB bus powered even after the PC is shut off. Shuttle support says: by design, can't disable this feature, newer mobo's do this (this is fricken' news to me, but I can't do much about it now).

    I have a hub connected to one of the USB ports where things like my GPS, etc. (6 devices) are connected to. As I found out today (the first time I didn't power the car up first thing in the morning) - this is causing a huge drain on my battery . So, I am looking for a creative solution.

    Any ideas? Is there anyway I can wire something in (somewhere!) that will force maybe just a disconnection of the USB hub after the key is removed? Or maybe, something wired into the USB extension cable that allows power to go to the hub but is then automatically turned off - disconnecting power to the hub - after the OPUS shuts down the PC? I have no idea if this is possible, so I'm looking to you...If this later one could somehow work, I think it'd satisfy all needs...don't know. please help.

    TIA,
    Per

  2. #2
    Variable Bitrate
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    You can put an inline switch between the battery and computer that would cut the main power to the computer. Doing so would effectivly turn off the USB ports.
    2003 Subaru Impreza TS
    Staus: Done.. too lazy to make pictures lol.

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    Maximum Bitrate S4Per's Avatar
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    Thanks for the quick response...Hmm. how would that work with the OPUS? For example, I remove the key, the OPUS is configured to run for another 10 seconds and then gracefully shut down the PC. What would I trigger this inline switch off of so all of that could happen?

    Thanks again..

  4. #4
    Variable Bitrate
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    The simplest way... Youd have to just wait for it to go off and then cut power. Im not sure on this next idea, I havent tried it but I think I might because I also dont want the constant drain on my battery

    The other option would be to get ANOTHER shutdown controller that monitors a drop the ACC line and when it drops below the normal crank voltage it triggers a switch that will cut the main power. Again I dont know if this is possible but I would like to know if it is so that I could do it.
    2003 Subaru Impreza TS
    Staus: Done.. too lazy to make pictures lol.

  5. #5
    FLA gospeed.racer's Avatar
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    Why not just use a simple relay?
    2005 Ford Focus ST

  6. #6
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    Please tell me more gospeed.racer, as I've never made it a secret that I'm just learning the majority of the electronics world ;-).

    Can you elaborate on what you mean?

    TIA,
    Per

  7. #7
    FLA gospeed.racer's Avatar
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    Why not just use a simple relay? Could you wire a relay to a "fan" header on the motherboard, and so whenever the board finally shuts down it opens the relay cutting the power to the hub?

    I am not certain the draw of a small relay, its just a thought.

    sorry about the double post....grrr.....i clicked the wrong button, lots of times
    2005 Ford Focus ST

  8. #8
    What can I say? I like serial. Curiosity's Avatar
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    If you have a 5V jack on the USB hub, you can connect that to the Opus (that has a 5V output right?). When something is connected to the jack on the hub, it disconnects the inline power to it. Or is the Opus always powered? If so, use a 5V supply connected to the ACC maybe?

  9. #9
    FLA gospeed.racer's Avatar
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    Ahhh...sorry. I assumed you were using a powered hub...if not, I agree, use a serperate 5v supply to the hub with whatever method of 5v supply you choose.
    2005 Ford Focus ST

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    @Curiosity - that's where I started. I have a 5v line running back from the hub to the Opus, but it caused some weird results in and of itself (see any of my posts yesterday - basically power was circling back to the mobo making it not think it was powered off when it really was...i need to do a couple of more tests on that one..it's fuzzy right now). But - even in that scenario, the USB bus is still powered, so power still goes to the hub and I have the problem we're talking about.

    Thanks for all of the suggestions...keep 'em comin'! ;-)

    @gospeed.racer - the hub uses bus and can use external power. i need the external to properly power all devices..

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    @Curiosity - I think the hub will still accept power from the bus even when something is plugged into the 5v jack.

    Is it possible to disable a hub from utilizing / accepting bus power?

  12. #12
    What can I say? I like serial. Curiosity's Avatar
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    Is it possible to disable a hub from utilizing / accepting bus power?
    Cut the red wire! Seriously, but open the hub and cut the trace coming from the computer's power (usually the red wire).

  13. #13
    FLA gospeed.racer's Avatar
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    I "think" the hub is probably set up to open a set of contacts to keep the 5v supplies from fighting. Kinda like when you plug in a set of headphones to a headphone jack and it cuts off the speakers. This may not be true, but I would think they would have to. You may end up having to trim the 5v+ wire going to the usb. Here is a very (ready VERY!!!) basic drawing of how I would try hooking it up. I found a website with this info..."The maximum current the fan headers can provide is 0.5A. The maximum 12v fan power that the motherboard can support on each header is 6W"....which tells me a relay should be no sweat for it. But again, I would like to hear from the electronic guru's here to be safe.
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    2005 Ford Focus ST

  14. #14
    Variable Bitrate
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    Speed Racer

    Could that be done with the main 12v line from the battery to the computer. Id much rather cut power there AND the USB hub power supply. How would i go about doing that?
    2003 Subaru Impreza TS
    Staus: Done.. too lazy to make pictures lol.

  15. #15
    FLA gospeed.racer's Avatar
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    Not sure that I follow completely. My idea was to use the fan header to turn off the power to the hub...are you asking about using the 12v to the board to kill the usb? in that case I would think so. If you want to cut all power on the 12v line to the pc, I would not recommend a relay, it will be huge and will be more difficult to wire up.
    2005 Ford Focus ST

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